1. Field of the Invention
This invention relates to an abrasive tape to be used for polishing of a magnetic head, or the like. This invention particularly relates to an abrasive tape to be used for finished polishing of a rough-polished surface of a magnetic head, or the like. This invention also relates to a method for polishing a magnetic head, wherein the abrasive tape is employed.
2. Description of the Prior Art
Video or high-grade audio magnetic heads are made by being polished with abrasive tapes. The abrasive tape comprises a flexible substrate, and an abrasive layer overlaid on the flexible substrate. In order for the abrasive layer to be provided, an abrasive composition containing abrasive grains, a binder, additives, and the like, is applied onto the flexible substrate and dried.
In general, when the surface of a magnetic head, or the like, is to be polished with the abrasive tape, two reels are positioned with the magnetic head, or the like, intervening therebetween. The abrasive tape is moved between the two reels while it is in contact with the surface to be polished. The abrasive tape is flexible and can snugly fit to a curved surface. Therefore, the abrasive tape is more suitable for the polishing of the curved surface of the magnetic head, or the like, than grinding wheels. Also, the abrasive tape can achieve scratch-free, accurate polishing of the surface to be polished, and is therefore indispensable to finish polishing of a rough-polished surface.
As is well known, polishing processes wherein the abrasive tape is used are carried out for the purposes of shaping the tip of a magnetic head into a desired form, eliminating the chipping of a magnetic head, and polishing the surface of a magnetic head to a smooth finish. In order for the polishing process to be performed in the most effective manner, it is required that the polishing performance be increased, the time required for the polishing be minimized, and that the smoothness of the polished surface be increased. In order for the polishing performance to be increased, an abrasive tape provided with hard, large-sized abrasive grains may be used. However, when the abrasive tape provided with hard, large-sized abrasive grains is used, the smoothness of the polished surface cannot be increased. On the contrary, in order for the smoothness of the polished surface to be increased, an abrasive tape provided with soft, small-sized abrasive grains may be used. However, the polishing performance of the abrasive tape provided with soft, small-sized abrasive grains is low. Therefore, various attempts have been made to provide an abrasive tape which would satisfy both of the incompatible requirements described above. For example, it has been proposed in Japanese Unexamined Patent Publication No. 54(1979)-97408 to employ two types of abrasive grains as the abrasive grains contained in the abrasive layer of an abrasive tape, thereby to increase both the polishing performance of the abrasive tape and the smoothness of a polished surface.
In recent years, information is recorded at an increasingly higher density on magnetic recording media, such as video tapes, and therefore magnetic heads are required to exhibit better recording characteristics. For example, the shortest recording wavelength was approximately 1 .mu.m for conventional video tapes, and is as short as 0.8 .mu.m for the S-VHS system video tapes (such as S-MASTER supplied by Fuji Photo Film Co., Ltd. and 5516XTS supplied by Sumitomo 3M Ltd.). As the recording wavelengths are shortened, it is required to improve the characteristics of the magnetic heads. However, the abrasive tape proposed in, for example, Japanese Unexamined Patent Publication No. 54(1979)-97408 is designed to polish magnetic heads to be used with recording wavelengths of approximately 1 .mu.m, and is not suitable for the polishing of magnetic heads which are recently required to exhibit better recording characteristics.
Also, recently, structures and materials of video heads are markedly varied from those of conventional ferrite video heads. For example, VTR NV-FS900 supplied by Matsushita Electric Industrial Co., Ltd. is provided with a laminated type of amorphous head, which is constituted of a combination of a ceramic material, an amorphous material, and a glass material. VTR CCD-TR55 supplied by Sony Corp. is provided with a MIG head, which is constituted of a combination of a ferrite material, a Sendust material, and a glass material. Also, VTR VTS625 supplied by Hitachi, Ltd. is provided with an amorphous head, which is constituted of a combination of a ferrite material, an amorphous material, and a glass material and which has a cross shape. Such video heads have compound structures in which materials having markedly different hardnesses are located adjacent to one another. Abrasive tapes used for the finish polishing of such video heads must be capable of polishing the video heads uniformly such that no difference in level such as a step at a boundary between a soft material and a hard material. A difference in level, which occurs between different materials, has various adverse effects. In particular, if a difference in level occurs at a video head gap part for magnetically carrying out signal recording and reproduction, the magnetic recording and reproducing characteristics of the video head will deteriorate. In high-performance video heads which are supplied recently, soft metals are used at the video head gap parts. Therefore, during the polishing operation, the video head gap part is worn more easily than the surrounding substrate parts, and a concave difference in level thereby occurs. Accordingly, space loss occurs, and the input-output transfer characteristics of the magnetic recording deteriorate.